Cold cathode discharge device



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Patented Apr. 1, 1952 UNITED STATES PATENT OFFICE GOLD CATHODE DISCHARGEDEVICE Application May 26, 1950, Serial No. 164,318

(Cl. 31 --2s) 8 Claims. 1

This invention relates to gaseous-discharge devices and moreparticularly to cold cathode gaseous-discharge devices of the type whichmay be used as voltage regulators.

In voltage regulators of the type generally used, a cold cathodegaseous-discharge device is utilized, the characteristic of the cathodebeing such that the current density at the cathode and hence the cathodedrop remain substantially constant for wide variations of current flowthrough the device. The constant current density is accomplished bymaking the cathode surface substantially homogeneous such that thecathoil spot increases or decreases in the area in proportion to thecurrent drawn.

Previously, attempts to use molybdenum as the cathode material haveproved unsatisfactory since the surface of the molybdenum becomescontaminated by the gas or due to contamination of the metal itselfwhereby the cathode surface is rendered non-homogeneous. As a result,the cathode spot during discharge tends to remain constant in size orthe area thereof varies as a non-linear function of the current,'therebyvarying the cathode fall with current variations, thus making the deviceuseless as a voltage regulator.

Thisinvention discloses a method of processing a molybdenum cathodedischarge device which will cause the device to be operative as-avoltage regulator over a long period of time.

Briefly, the invention comprises positioningthe electrode elements inthe device, filling the device with a gaseous medium, and sealing thedevice. Following this, a glowdischarge is produced between .the cathodeand another element of the device, for example, the anode, saiddischarge being of suflicient magnitude to cause substantial sputteringof the cathode. The sputtered par.- ticles become attached to the otherelements of the tube, for example, the anode and support structures, aswell as portions of the tube envelope. In addition, some particlesreturn to the cathode. The result is that the sputtered Particles reactwith the gas to remove any contaminating material therefrom.Continuation of the sputtering process long enough will produce a cleangaseous medium and a clean cathode sur- On this surface, the currentdensity of the glow spot will remain substantially constant with thearea of the spot increasing or decreasing in proportion to the currentflow. Such a device once properly processed will retain its voltageregulating characteristic for an extremely long time, for example, inexcess ;of five thousand hours.

In addition, if desired, a getter may be utilized to initially clean thegas prior to the sputtering process.

.Other and further advantages of this invention .will .be apparent asthe description thereof progresses, reference being had to theaccompanying drawing, wherein:

Fig. 1 illustrates a longitudinal, cross-sectional view of anelectron-discharge device constructed and processed in accordance withthe invention; and

Fig. 2 illustrates a transverse, cross-sectional view of the deviceshown in Fig. 1 taken along line 2-2 of Fig. 1.

Referring now to Figs. 1 and 2 of the drawins, there is shown agaseous-discharge device comprising a glass envelope I0 having a basesection H. Extending upwardly from base section I l is a glass press 12through which extends a pair of lead-in members I3 and I4. Lead-inmember 13 is attached to a rod 15 which constitutes the anode of thedevice, said anode being substantially coaxial with envelope l0 and maybe made, for example, of nickel. Lead-in member [4 has attached theretoa substantially cylin- .drical member 16 which surrounds the anodemember 15, member l6 comprising the cathode and being made in accordancewith this invention of molybdenum.

Positioned above cathode member 5 is a mica spacer member I! whichengages anode rod l5 and the sides of envelope 10, thereby positioninganode rod 15 coaxially with envelope Ill and coaxially with cathode I6.A second mica spacer I8 is positioned above spacer l1 and supports agetter structure comprising a U-shaped support member I9 to which isattached a bar of getter material 20 which may be flashed, for example,by induction heating. Member [9 is supported by a pair of uprights 2|attached to mica spacer I8 and the entire getter assemb y on mica spacerI8 is rigidly positioned above mica spacer I] by a metallic grommet 22extending through spacers I1 and I8 and surrounding the upper end ofanode rod l5 and rigidly engaging said anode.

An exhaust tube .23 extends downwardly from press l2 whereby the tubemay be exhausted and filled with the discharge medium following whichthe end of tube 23 is sealed. Leads l3 and I4 extend downwardly througha base 24 which may be, for example, ceramic or glass and terminate incontacts 25 and 26, respectively. Base 24 is supported in a metallicholder 21 which is attached to a metallic shield 28 surrounding envelope1-0.

The tube elements are first assembled and inserted in envelope it. Theenvelope 10 is then evacuated and refilled with the desired gas mixturewhich comprises, for example, neon and argon in the proportion ofninety-nine per cent neon and one percent argon. It has been found thata desired pressure for the gaseous medium is on the order of sevencentimeters of mercury.

The getter assembly I9 is then flashed, for example, by inductionheating to cause a preliminary clean-up of the gaseous filling. Ifdesired, this getter operation may be eliminated by the ,use of [asuitably pure gaseous filling and adequate outgasing of the tubestructure prior to filling with the gas. A discharge is now producedbetween the cathode l6 and the anode l sufilclent to produce sputteringof the cathode. A suitable voltage for this comprises two hundred andtwenty volts A. C. R. M. S. with the negative portion of the cycleeliminated, for example, by clipping.

The current through the device is then 'adjusted by adjustment of asuitable load resistor in series with the discharge device and thevoltage source to an average current on the order of forty milliamperes.For this condition, a peak current as high as one hundred and sixtymilliamperes will be produced. The particular currents cited herein willvary for the particular dimensions of the cathode surface, and asdisclosed herein are for a cathode utilized'in a miniature voltageregulator.

The glow discharge causes particles of molybdenurn'to be sputtered fromthecathode surface, said particles reacting with the gaseous filling toremove any impurities such as oxides therefrom, said oxides being lockedup or occluded by the particles. These particles collect on the otherelements of the tube and the envelope, as well as on the cathode itself.

The sputtering operation is continued for a suificient length of time toexposed a clean surface on the cathode and to completely clean thegaseous filling. It has been found that to accomplish the completecleaning operation, a period on the order of one to two hundred hours ofconstant sputtering is necessary. When the gas and the cathode surfaceare completely cleaned, it has been found that the tube does not becomerecontaminated by action of the gaseous filling on the envelope ID, aswas previously believed. Therefore, it is immaterial whether the insideof envelope l0 becomes covered with the sputtered material, and indeed,it is desirable that the sputtered material return in large part to thecathode surface. The use of a cathode surrounding the anode is conduciveto the return of the sputtered material to the cathode surface.

Further, since the cathode surrounds the anode, a large area is exposedto the anode surface thereby producing a device which is capable ofcarrying relatively high currents for a tube of this size.

This completes the description of the particular embodiment of theinvention illustrated hereirr. However, many modifications thereof willbe apparent to persons skilled in the art. For example, any desiredgaseous medium may be used for filling the envelope 1.. The envelope I0need not necessarily be made of glass, but could be metal or othermaterials. The electrode assembly could be modified, if desired, toinclude any number of grids or auxiliary electrodes. invention be notlimited to the particular details of the embodiment described herein,except as defined by the appended claims.

What is claimed is:

1. The method of processing a molybdenum cathode gaseous-dischargedevice comprising filling the envelope of said discharge device with agaseous medium, sealing off said envelope before producing any dischargeof said device, and maintaining a discharge between said cathode andanother electrode of said device for a period sufiicient to clean saidcathode surface.

2. The method'of processing a molybdenum cathode gaseous-dischargedevice comprising fill- Therefore, it is desired that this ing theenvelope of said discharge device with a gaseous medium, sealing offsaid envelope before producing any discharge of said device, andmaintaining a glow discharge between said cath-' ode and anotherelectrode of said device for a period sufficient to clean said cathodesurface.

3. The method of processing a gaseous-dis charge device having an anodeand a molybdenum cathode comprising filling the envelope of saiddischarge device with a gaseous medium,

sealing off said envelope before producing any discharge of said device,and maintaining a discharge between said cathode and said anode for aperiod sufiicient to clean said cathode surface.

4. The method of processing a gaseous-discharge device having an anodeand a molybdenum cathode comprising filling the envelope of saiddischarge device with a gaseous medium, scaling 011 said envelope, andmaintaining a discharge between said cathode and said anode for a periodsufficient to clean said cathode surface, the magnitude of saiddischarge being sufiicient to produce substantial sputtering of saidcathode surface.

5. The method of processing a gaseous-discharge device having an anodeand a molybdnum cathode comprising filling the envelope of saiddischarge device with a gaseous medium comprising neon, sealing off saidenvelope, and maintaining a glow discharge between said cathode and saidanode for a period sufiicient to clean said cathode surface, themagnitude of said discharge being sufficient to produce substantialsputtering of said cathode surface.

6. The method of processing a molybdenum cathode gaseous-dischargedevice comprising filling the envelope of said discharge device with agaseous medium, sealing off said envelope, and maintaining a dischargeof suflicient magnitude to cause sputtering of said cathode between saidcathode and said anode for a total period in excess of one hundredhours.

'7. The method of processing a molybdenum cathode gaseous-dischargedevice comprising filling the envelope of said discharge device with agaseous medium, sealing off said envelope, and maintaining a dischargebetween said cathode and another electrode of said device for a periodsufiicient to clean said cathode surface, the

magnitude of said discharge being sufficient to ,produce substantialsputtering at said cathode PAUL W. STUTSMAN;

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name 'Date 1,720,172 Dessauer July 9, 19291,927,812 Thomson Sept. 19, 1933 2,290,208 Quarrie July 21, 19422,440,154 Oles .Apr. 20, 1948

